Fitter needs wherewithal when struggling to remove both weights (9)
I believe the answer is:
healthier
'fitter' is the definition.
('healthy' is associated in meaning with 'fit')
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for healthier that I've seen before include "More in the pink" , "less prone to disease" , "Fitter" .)